-LRB- CNN -RRB- -- One of the three guns Adam Lanza used to kill 20 children and six adults at an elementary school in Newtown , Connecticut , was a military-style semiautomatic rifle known as an AR-15 . That surprised and shocked a lot of people unfamiliar with America 's gun culture . They questioned why such weapons are available and why anyone would need them .

`` Personally I do n't know how any ordinary citizen can justify owning an automatic or semiautomatic gun , '' writes CNN commenter Mark Smerkanich . `` Ca n't we leave those guns to the trained military ? ''

Self-described gun owner Julie Jones-Hawkins comments , `` I ... fully support a ban on rapid-fire weapons . Any weapon that can take out an entire kindergarten class is a problem . ''

Here are five reasons many gun owners say they want military style rifles :

` Some people play golf , others bowl . I shoot '

`` Every month or so I take my guns out to the range and shoot . It 's thrilling , exciting and a great way to vent , '' says Christopher L. Kirkman , a Florida-based military-style gun owner .

Kirman was one of more than 100 gun enthusiasts who shared opinions on CNN iReport about owning firearms that would have been banned under the now-expired 1994 federal weapons ban .

`` Sure , I could try to say that the reason I own these guns is self-defense , but the truth of the matter is that , although they will technically serve this purpose , they are not why I own them , '' he says .

Michigan gun owner Ethan Daniels describes his enthusiasm for his rifle more succinctly , saying , `` I like to shoot , and that is one heck of a fun carbine to plink with . ''

iReport : Tell us why you own your military-style weapon

Background can factor into a gun owner 's choice of weapon . `` The AR-15 is what I am used to from my extensive training as an airborne infantryman , '' writes Nathan Lee . `` Because of my training , it 's what I feel the most comfortable with . ''

Another reason for these guns is hunting . The AR-15 is a `` good hunting platform . I 've hunted coyote with it , '' says CNN iReporter MVR155 , who owns two of the weapons . He asked to remain anonymous .

Owners of military-style rifles also use them to hunt deer and other game . But some states have banned the AR-15 and its .223 caliber for deer hunting .

Related : Newtown shooter 's guns : What we know

` It 's cool '

It may not be the best or most important reason , but military-style weapons often appeal to the enthusiast side of the American gun owner . Just like many car lovers who dream of owning a Lamborghini , many gun owners get excited about the idea of owning an AR-15 .

`` There are people who buy certain types of firearms because they have a certain image -- the AR-15 is one of them , '' says Austin Nikel , a former AR-15 owner in Boulder , Colorado .

`` One thing about this country is how Hollywood has glorified the image behind those certain types of weapons . A lot of guys grow up with GI Joe , and that image is extremely attractive . It grabs you and affects you .

`` A lot of people buy the AR-15 because , well , it 's cool . ''

Apparently it was n't cool enough for Nikel to hold on to . He ended up selling his AR-15 to his father .

iReport : Why some own military-style weapons

' A part of history '

`` Since coming of age -- and in the decades since -- I have collected many different firearms , some of them historical pieces , some for sport , some of them even the so-called ` assault weapons ' that are now a controversy , '' says iReporter Hrothgar01 .

`` Guns like these are as much a part of the history of this country as the muskets carried by pioneers , the rifles toted by doughboys in the trenches , and the other arms that have served and protected throughout the years . To hold one in your hands , appreciate its history and design , and to be able to take that piece of history to the range and work -- it is a feeling that many people in this debate do not understand or appreciate . ''

Related story : By the numbers : Guns in America

` Protecting my family '

`` I believe the foremost person responsible for protecting my family and myself is me , '' writes iReporter ShortyDoowap , who owns a pair of AR-15s . `` These rifles provide me with the tools to perform that duty . I do n't own these guns to target shoot , though I do that with them . I do n't hunt with them , though I could in a pinch . ''

Parks says he `` would not hesitate to use one to simply defend my home and family from a single intruder if it became necessary . ''

Related : Parents defend right to keep guns in the home

In some home-protection situations , fans say military-style rifles are generally more accurate than handguns . Rifles are generally easier to learn how to shoot , say military-style rifle owners .

Like most firearms , military-style weapons such as the AR-15 are semiautomatic -- increasing protection because the shooter can fire off many shots without having to manually chamber a new bullet . With a bolt-action rifle or pump-action shotgun , firing multiple shots takes more time .

`` When you weigh it all out , these types of guns are stigmatized , '' says iReporter MVR155 . Military-style weapons look more dangerous than other guns , he says , but really , there are many weapons available which are just as lethal , but which are not designed in a military style .

iReport : One gun owner 's solution

` Fascination with the Second Amendment '

`` I am a proud owner of an AK-47 , '' writes iReporter INGunOwner . `` It 's a terrific gun . Lots of fun to shoot . I own an AK because of my fascination with the Second Amendment , which I view as a backstop protector of freedom . Many people would argue that we have no use for it today because the government is trustworthy .

`` However since it acts as a deterrent , we can never measure exactly how much it has been effective . Perhaps the notion that people feel safe with our government after over 200 years is a testament to the Second Amendment value in balancing power with the citizens . ''

Related : Gun owners fear new legislation could tread on their rights

CNN 's Henry Hanks contributed to this report .

@highlight

A military-style rifle was used in the Newtown , Connecticut , school shooting

@highlight

`` Ca n't we leave those guns to the trained military ? '' asks a CNN commenter

@highlight

Many gun owners collect them , using them for hunting , target shooting and protection

@highlight

`` A lot of people buy the AR-15 because , well , it 's cool , '' says a former owner